1.\" Copyright (c) 2005 Robert N. M. Watson 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd January 21, 2008 28.Dt SCHED_4BSD 4 29.Os 30.Sh NAME 31.Nm sched_4bsd 32.Nd "4.4BSD scheduler" 33.Sh SYNOPSIS 34.Cd "options SCHED_4BSD" 35.Sh DESCRIPTION 36The 37.Nm 38scheduler 39is the traditional system scheduler, providing both high throughput and solid 40interactive response in the presence of load. 41.Pp 42The following sysctls are relevant to the operation of 43.Nm : 44.Bl -tag -width indent 45.It Va kern.sched.name 46This read-only sysctl reports the name of the active scheduler. 47.It Va kern.sched.quantum 48This read-write sysctl reports or sets the length of the quantum (in 49micro-seconds) granted to a thread. 50.It Va kern.sched.ipiwakeup.enabled 51This read-write sysctl sets whether or not the scheduler will generate an 52inter-processor interrupt (IPI) to an idle CPU when a thread is woken up. 53Otherwise, idle CPUs will wait until the next clock tick before looking for 54new work. 55.It Va kern.sched.preemption 56This read-only sysctl reports whether or not the kernel is configured to 57support preemption, which reduces the latency to run lower priority threads 58on wakeup. 59.El 60.Pp 61Some sysctls will be available only on systems supporting SMP. 62.Sh SEE ALSO 63.Xr sched_ule 4 , 64.Xr sysctl 8 65.Sh HISTORY 66The 67.Nm 68scheduler has been present, in various forms, since the inception of 69.Bx . 70.Sh BUGS 71While a highly robust and time-tested scheduler, 72.Nm 73lacks specific knowledge of how to schedule advantageously in non-symmetric 74processor configurations, such as hyper-threading. 75